Carbonaceous chars which are capable of functioning as catalysts per se are well known. The presence of charcoal has been known to enhance a variety of oxidation reactions, including the oxidation of hydrogen sulfide and SO.sub.2. In those instances where a carbonaceous char has been observed to affect such reactions, it has functioned generally as a true catalyst, i.e. it affects only the rate of a given reaction but is not itself changed by the reaction to any significant degree.
Carbonaceous chars prepared from nitrogen-rich starting materials have been known to be much more effective in catalyzing certain reactions, such as hydrogen peroxide decomposition, than those prepared from nitrogen-poor feed stocks. Similarly, enhanced catalytic properties are known to be imparted into chars prepared from nitrogen-poor starting materials by exposing such chars to nitrogen-containing compounds such as ammonia at high temperatures. More recently, catalytically-active chars have been prepared by the calcination or calcination/activation of low- or high-temperature chars prepared from nitrogen-rich materials such as polyacrylonitrile and polyamide. (For the purposes of this discussion, the term "calcination" will refer to heating at high temperatures under substantially inert conditions). Catalytically-active chars have also been prepared from nitrogen-poor starting materials by the calcination of high-temperature chars in the presence of nitrogen-containing compounds such as ammonia. In all cases, high-temperature carbonaceous chars are those produced by thermal treatment at temperatures greater than 700.degree. C. Low temperature carbonaceous chars have not been subjected to temperatures greater than 700.degree. C. Advantages have been found in oxidizing the high-temperature char prepared from nitrogen-poor feedstocks prior to or during exposure to nitrogen-containing compounds. Similarly, oxidizing a low-temperature char prepared from nitrogen-rich feed stocks such as polyacrylonitrile has been found to enhance the catalytic activity.
However, all of the prior art processes for preparing carbonaceous chars which are catalytically active per se have certain disadvantages which limit their overall utility and practicality. For example, nitrogen-rich starting materials, such as polyacrylonitrile or polyamide, are expensive and have been found to generate large amounts of cyanide and other toxic gases upon carbonization. Those processes which use chars derived from nitrogen-poor starting materials invariably use high temperature chars, such as activated carbons, which require further processing. Since such materials are fairly inert chemically, the use of extensive and aggressive chemical post-treatments is usually required to effect significant changes in their catalytic capabilities. In so doing, such changes are usually brought about only at the expense of carbon yield as reflected in the density of the final product at a given level of catalytic activity. The use of high-temperature chars is, therefore, inevitably more expensive than the direct use of the raw materials from which they are derived. Additionally, such prior art processes entail the use of large amounts of toxic and/or hazardous reagents such as nitric acid, sulfuric acid, or ammonia, and the generation of significant amounts of toxic and/or hazardous byproducts such as sulfur dioxide, nitric oxide, and cyanide.
Accordingly, it is the object of the present invention to provide an improved process for the manufacture of a catalytically-active carbonaceous char wherein the carbonaceous char catalyst is prepared directly from an inexpensive and abundant nitrogen-poor starting material such as a bituminous coal or a material having bituminous properties. It is further the object of the present invention to limit the use of agents responsible for imparting catalytic activity to the char by performing the essential treatments during the low-temperature transition of the starting material to the final product. These treatments include oxidation of the low-temperature char, preferably by inexpensive, abundant, and relatively non-toxic oxidants, and exposure of the oxidized, low-temperature char to small amounts of inexpensive, abundant,and relatively non-toxic nitrogen-containing compounds prior to or during, not after, the initial calcination and resulting condensation of the carbon structure. By this method carbonaceous chars with high catalytic activity per se for a variety of chemical reactions, including, but not limited to, the conversion of peroxides, chloramines, sulfides, sulfur dioxide and nitric oxide, can be manufactured relatively inexpensively and conveniently, with minimal departure from conventional processes for the manufacture of high-temperature carbonaceous chars such as activated carbons and cokes.